Spain's National Court is to question two senior officers from Catalonia's regional police force and the leaders of two pro-Catalan independence civic groups who have been placed under investigation for sedition.

Spain's National Court is to question two senior officers from Catalonia's regional police force and the leaders of two pro-Catalan independence civic groups who have been placed under investigation for sedition.

The court said on Wednesday that the four will be quizzed on Friday about their roles in demonstrations in Barcelona on September 21 and 22 when Spanish police arrested several Catalan government officials and raided offices in a crackdown on preparations for last weekend's referendum on Catalonia's independence.

Spanish authorities said the demonstrations hindered the police operation. During the rallies, there were some disturbances and two police vehicles were wrecked.

The four include regional police chief officer Josep Lluis Trapero and Jordi Sanchez, the head of the Catalan National Assembly, which has been the main civic group behind the independence movement.